This invention relates to an apparatus for and method of transferring substrates, such as semiconductor wafers or LCD (Liquid-Crystal Display) glass substrates, between a cassette and a processing section.
In general, photolithography has been used to form circuit or electrode patterns on a substrate, such as a glass substrate, in the manufacture of liquid-crystal displays (LCDs). In photolithography, a series of processes is performed. The processes include cleaning a substrate, drying the substrate, forming a resist film on the substrate, exposing the resist film, and developing the resist film. In the processing units which carry out the processes, a substrate taken out of a cassette in a cassette station and placed on an arm is transferred to the processing sections, which subject the substrate to a series of processes, including the cleaning of the substrate. The substrate passed through the processing sections is put on the arm again and returned to the cassette.
At the top face of the arm, for example, when the section that supports the substrate before cleaning is the same as the section that supports the substrate after the cleaning, the following problem arises: the contaminants on the back of the substrate stick to the support member via the top face of the arm when the uncleaned substrate is put on the arm, which permits the contaminants to stick to the back of the cleaned substrate again when the cleaned substrate is placed on the arm and transferred. As means for solving the problem, a substrate transfer apparatus has been disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 5-152266. With the substrate transfer apparatus in Jpn. Pat. Appln. KOKAI Publication No. 5-152266, a substrate takeout arm which takes an uncleaned substrate out of a cassette and transfers it to the cleaning section is constructed of one unit and a cleaned-substrate storage arm which returns the substrate cleaned in the cleaning section to the cassette is constructed of a separate unit. This prevents contaminants from sticking to the substrate again.
With the substrate takeout arm and cleaned-substrate storage arm being constructed of separate units, however, the substrate transfer apparatus has disadvantages in that it requires the takeout arm and storage arm separately and that the driving unit for switching between the takeout arm and storage arm is relatively large and therefore the configuration is complicated. Furthermore, there is another problem: the turning of the entire arm accompanying the switching action requires a substantially wide space, which prevents effective use of the apparatus installation space.